Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for performing a contention-based random access procedure over a contention-free random access procedure based on listen-before-talk (LBT) in a wireless communication system.
Related Art
3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
The fast uptake of LTE in different regions of the world shows both that demand for wireless broadband data is increasing, and that LTE is an extremely successful platform to meet that demand. At the same time, unlicensed spectrum has been more considered by cellular operators as a complementary tool to augment their service offering. Unlicensed spectrum can never match the qualities of the licensed regime. However, those solutions that allow an efficient use of unlicensed spectrum as a complement to licensed deployments have the potential to bring great value to 3GPP operators, and, ultimately, to the 3GPP industry as a whole. Given the widespread deployment and usage of other technologies in unlicensed spectrum for wireless communications in our society, it is envisioned that LTE would have to coexist with existing and future uses of unlicensed spectrum. Existing and new spectrum licensed for exclusive use by international mobile telecommunications (IMT) technologies will remain fundamental for providing seamless coverage, achieving the highest spectral efficiency, and ensuring the highest reliability of cellular networks through careful planning and deployment of high-quality network equipment and devices.
Complementing the LTE platform with unlicensed spectrum is a possible choice under these considerations, as it would enable operators and vendors to leverage the existing or planned investments in LTE/evolved packet core (EPC) hardware in the radio and core network, especially if licensed-assisted access (LAA) is considered a secondary component carrier integrated into LTE.
LAA may cause potential impact and/or issued on random access preamble transmission. Accordingly, a new mechanism to transmit a random access preamble in LAA environment may be required.